Samuel Grossman, BS Pharm, Pharm.D, CDE Answered 4/17/2015

The need to take insulin depends on the blood sugar, what kind of insulin you take, when you ate last, and when you will eat again. If you take long acting insulin at bedtime only, and ate the evening before and you are planning to fast the entire day and eat in the evening again, the dose of your long acting insulin should be reduced by about 50% to prevent low blood sugar. If you ate before sunrise and you are planning to fast all day and eat at sunset, the recommendation is to reduce the dose of your pre-meal insulin by about 50%. It is recommended that you do fingersticks more often during the fasting day to determine if you blood sugar is high or low. Consider consulting with your provider to determine what is the best way to treat your diabetes if you are fasting for that day